1. Field of the Invention
The present invention relates to a capsule rupture printing system for recording an image in an imaging sheet with a layer of subminiature capsules, and more particularly to a system comprising a cathode-ray tube which projects images or information to be recorded onto the imaging sheet.
2. Description of the Prior Art
A review of the prior art reveals a number of existing printing systems, namely; a thermotransferring printing system, an inkjet printing system and a xerography system.
The thermotransferring printing system selectively energizes plural heat generating elements which are disposed on a thermal head. Using the heat radiated from the selected heat generating elements, an ink on a surface of an ink sheet is melted. The ink is then transferred onto a sheet of recording paper for printing image and letter information.
In this system, a dot of ink corresponding to the area of one heat generating element adheres onto the sheet of recording paper and thereby producing one pixel. There are two methods for tone gradation printing according to this system: one is to repetitively print at one spot to change the density of a printed pixel; and the other is to change a printed area per unit area. However, using the former method is required in order a long time to obtain a tone gradation. According to the later method, the area of a pixel is large and therefore the quality of printed pixel is low. Furthermore, when full color printings are required, three printing processes for three different colors, cyan, magenta and yellow, are used in order to produce a color picture. As a result, there occurs a mis-superpose of colors in which three pictures of different colors are not perfectly superposed on top of the other. The result is that it takes a long time to produce a full color picture. The inkjet printing system has the same problems as those of the thermotransferring printing system.
Finally there is the xerography system, whereby an image or pattern is formed on a cylindrical sensitized or photoconductive drum whose outer surface is coated with a photoconductive material such as Se, ZnO, amorphous Si or an organic semiconductor. Areas on the outer surface of the photoconductive drum, which correspond to a desired image to be reproduced, are exposed to light, and electrostatically charged to form a latent image. The latent image is developed by using a toner, and the toner image is then transferred to paper. The xerography system described above is characterized by its capability of reproducing images at a comparatively high speed. However, since this system employs an optical system for producing the latent images on the photoconductive drum, it requires that the drum be made to extremely tight dimensional tolerances. Moreover, since the toner is always consumed, it is necessary to always store and supplement the toner. Accordingly, the cost of manufacturing the drum and the copying apparatus is considerably high. Further, the construction of the apparatus becomes complicated and the maintenance, thereof, troublesome.
In order to solve the above problems, imaging systems based on using a photosensitive sheet are known, F. W. Sanders et. al. U.S. Pat. Nos. 4,399,209 and 4,440,846 describes an imaging system wherein a photosensitive layer comprising microcapsules containing a photosensitive composition in the internal phase is image-wise exposed to actinic radiation and subjected to a uniform rupturing force whereupon the microcapsules rupture and image-wise release the internal phase. Image-forming agents such as substantially colorless chromogenic materials are typically associated with the microcapsules, so that when the microcapsules rupture, the chromogenic materials are able to image-wise react with a developer material and produce a color image. As the photosensitive composition encapsuled in microcapsules on the imaging sheet solidifies to varying degrees according to the amount of exposure to light, the amounts of chromogenic materials released from the capsules vary depending upon the degrees of exposure to the light. Consequently, a tone of the printed-out image can be changed. Isobe et. al. disclose in their Japanese laid-open Pat. No. 61-143738 a method to project an image displayed on a CRT display as shown in FIG. 7 onto an imaging sheet coated with the microcapsules, which is disposed adjacent to the display screen of the CRT display, and records its latent image on the imaging sheet. Unlike the xerography system, the Isobe system does not require a photoconductive drum for producing a latent image nor a toner, and therefore the apparatus can be manufactured at a low cost and in small size, and, of course, the maintenance for the drum and toner is not required. However, according to this system, light, emitted from a fluorescent material 16 coated on the inner face of a glass plate 17 composing a CRT display screen, pass through the glass plate 17, and then through a space between the CRT display screen and the imaging sheet, and reach the imaging sheet, and as a result, an image focused on the CRT display becomes out of focus on the imaging sheet.